Method of sealing spark plug electrodes in ceramic insulators



Aug. 8, 1944. J. A. JEFFERY 2,355,443

METHOD OF SEALING SPARK PLUG ELECTRODES IN CERAMIC INSULATORS Filed Feb.23, 1942 Jase 0f; A. Jeffery Elma/WM Patented Aug. 8, 1944 METHOD OFSEALING SPARK PLUG ELEC- TRODES IN CERAMIC INSULATORS Joseph A. Jeffery,Detroit, Mich, assignor to Champion Spark Plug Company, Toledo, Ohio, acorporation of Delaware Application February 23, 1942, Serial No.432,024

Claims.

This invention relates to spark plugs, and particularly to a method ofefiiciently sealing electrodes in the ceramic insulators thereof.

Considerable difficulty has been experienced in sealing electrode wiresin ceramic insulators either by heat shrinking a green insulator aroundan electrode, or by inserting the electrode into a matured insulatorwith or without a sealing medium.

In the case of the green insulator, the shrinkage from firing isconsiderable both longitudinally and latitudinally 0f the insulator, andas a result the electrode wire may be too loosely fastened to provide atight joint, or it may be so tightly fastened as to cause the insulatorto split or set up weakening strains therein. In the case of the firedinsulator, there is no opportunity to shrink the insulator on the wireand sealing mediumsmust, therefore, be employed.

The object of the present invention is to obviate these objections bythe provision of a method of sealing electrode wires in ceramicinsulators, which is simpl and economical to perform and effects anefiicient sealing thereof by shinkage without the use of separatesealing mediums and without causing a splitting of the insulator orsetting up injurious strains therein.

The invention is fully described in the following specification, andillustrated by the accompanying drawing, in which- Figure 1 is a centrallongitudinal section of an initially fired or partially shrunk insulatorwith an electrode positioned in its bore and showing a slight free spacebetween the insulator and bore Wall, and Fig. 2 is a similar viewthereof after the final firing or shrinking operation, showing theinsulator and electrode in intimate sealed contact.

My method consists in prefiring the ceramic insulator I without theelectrode wire 2 therein until all but a very small amount of theshrink-'- age has been removed therefrom. The electrode is' theninserted into the insulator bore, with which it has a free sliding fit,as indicated by the space 3, and the insulator is then given a finalfire to maturity, which fire is preferably of a rapid nature. Theinitial firing leaves enough shrinkage in the insulator to bring aboutan efliicient tight sealing of the electrode wire therein during thefinal firing withoutsetting up harmlul strains and stresses in theinsulator material.

The purpose of the rapid final firing after the electrode has beeninserted is to prevent the recrystallization and consequent roughsurface of the electrode, which is produced with a pro- 66 longed firingand particularly with a firing necessary to fire a green insulator andshrink it onto an electrode. The present method is also found to reduceor avoid the objectionable longitudinal scoring of the electrode, suchas is frequently caused where a green insulator is shrunk onto anelectrode by a single firing.

I It will, of course, be understood that whenever considered necessaryor desirable, a wetting agent or melting flux may be applied to theinsulator or electrode, or both, to provide a more intimate contactbetween the members.

In practice, the electrode used in connection with a ceramic insulatoris usually of platinum, or its alloys, inasmuch as most other metalsusable for electrodes oxidize and disintegrate, or else melt and flow,at th temperatures encountered in the final shrinking of a ceramicinsulator onto an electrode wire. It is thus apparent that the metal oralloy for the electrode should be of a nature, or be treated, towithstand oxidizing and should withstand melting at maturing temperatureof the body to which it is joined, and also that its co-efilcient ofexpansion should be similar to that of the insulator.

The following is an illustration of an efficient manner of performingthe method where an insulator body of such material as described in myapplication for patent Serial No..210,466, filed May 2'7, 1938, nowPatent No., 2 ,274,067, dated February 24, 1942, is used in connectionwith a platinum electrode of approximately .051" diameter: The unfiredinsulator body, provided with an electrode-receiving bore ofapproximately .059" diameter, and fired for approximately six hours at atemperature of approximately 2900 F., will shrink sufiiciently to reducethe bore to approximately .052" diameter. The electrode is then properlypositioned in the bore and the insulator is quickly brought up to atemperature of approximately 2950 F. and held there for approximatelytwo'hours. This causes the bore diameter to be reduced to approximately.050", thus giving the equivalent of approximately a .001"

press fit, which is very satisfactory.

trode wire to be inserted in the bore, will produce an advantage overthe common method of sealing wires in insulators wherein only a singlefiring oi the insulator to maturity is practiced and the wire isdisposed in the insulator during the entire firing.

Having thus described my invention, what I claim as new, and desire tosecure by United States Letters Patent, is:

l. The method of sealing an electrode in the bore of a ceramic insulatorfor a spark plug and wherein the electrode is smaller in diameter thanthe bore of the green insulator, which consists in initially firing thegreen insulator to an extent slightly short of maturity to shrink thebore a predetermined extent so that the electrode has a sliding fittherein, then positioning the electrode in the bore, and giving theinsulator a final fire to maturity to shrink the bore of the insulatorinto intimate and sealing contact with the electrode therein.

2. The method of sealing an electrode in the bore of a ceramic insulatorfor a spark plug and wherein the electrode is smaller in diameter thanthe bore of the green' insulator, which consists in giving the greeninsulator an initial firing to an extent slightly short of completefiring shrinkage to partially reduce the size of its bore and then arapid final firing to maturity of shorter duration; than the initialfiring, and placing the electrode in the bore between the two firings,whereby it is sealed in the insulator by the resultant shrinkage fromthe final firing.

3. The method of sealing an electrode in the bore of a ceramic insulatortor a spark plug and wherein the electrode is smaller in diameter thanthe bore of the green insulator, which consists in giving the greeninsulator an initial firing to reduce the size of its bore by shrinkagea predetermined extent and then positioning the electrode in the borethen firing to maturity and sealing the electrode in the insulator bythe resultant shrinkage from the final firing, the initial firingreducing the bore diameter to within approximately .003 of an inch ofits final shrinkage diameter.

4. The method oi sealing an electrode in the bore of a ceramic insulatorfor a spark plug and wherein the electrode is smaller in. diameter thanthe bore of the green insulator, which consists reduce the'diameter 01'its bore from approximately .059" to approximately .052, then insertingan electrode wire in the bore with a clearance of approximately .001 ofan inch, and then giving the insulator a rapid firing to maturity toseal the electrode therein.

5. The method of sealing a platinum or platinum alloy electrode in thebore of a ceramic insulator for spark plugs and wherein the electrode issmaller in diameter than the bore of the green insulator, which consistsin giving the green insulator an initial firing of approximately sixhours to a temperature of approximately 2900" F. to reduce by shrinkagethe size of its bore a predetermined extent, and then subjecting theinsulator to a final firing to maturity, wherein it is quickly broughtup to approximately 2950 F. and held there for approximately two hours,and positioning the electrode in the bore between the two firings,whereby it is sealed in the insulator by the resultant shrinkage iromthe final firing.

JOSEPH A. JEFF'ERY.

